There has been considerable research on increasing the productivity and electricity generation performance of a fuel cell.
For example, Patent Literature 1 discloses an aqueous catalyst paste composition for fuel batteries and a catalyst ink composition which are adequate in the dispersibility of a catalyst-supporting carbon material, low in viscosity, and superior in storage stability and the adsorption rate of a proton-conducting polymer, and which have the suitability to coating.
Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2016-122594
Patent Literature 2: JP-A No. 2010-238513
Patent Literature 3: JP-A No. 2004-113848
Patent Literature 4: International Publication No. WO2013/121781
Patent Literature 5: JP-A No. 2014-154225
Patent Literature 6: Japanese translation of PCT international application No. 2014-522552
However, the catalyst ink composition described in Patent Literature 1 has a problem in that it is difficult to secure both the viscosity of a catalyst ink and the electricity generation performance of a fuel cell produced by using the catalyst ink.